Thermally actuated control device having ceramic tubes with central heat expandible members



March 29, 1966 G. J. FAIRBANKS 3,243,557

THERMALLY ACTUATED CONTROL DEVICE HAVING CERAMIC TUBES WITH CENTRAL HEAT EXPANDIBLE MEMBERS Filed March 6, 1964 I //Y VIN/ 0f v I Gar-04:7 c/f Fan-100,45

,4 r y ar-ney United States PatentO 3,243,557 THERMALLY ACTUATED CONTROL DEVICE HAVING CERAMIC TUBES WITH CENTRA HEAT EXPANDIBLE MEMBERS Gordon J. Fairbanks, Indianapolis, Ind., assignor to Stewart-Warner Corporation, Chicago, 11]., a corporation of Virginia Filed Mar. 6, 1964, Ser. No. 350,054 6 Claims. (Cl. 200-137) This invention relates to switching means actuated by temperature fluctuations and more particularly to high temperature switches such as may be used in detecting open flames for use in furnaces or fire protection devices or the like.

It is an object of this invention to provide thermally operable switches which may be used to detect flames with little or no regard to corrosion or oxidation.

It is also an object of this invention to provide rugged switching structures.

A further object of this invention is to provide switching devices which are more economical than those presently available on the market.

In addition it is an object of this invention to provide a flame detector switch useful in a furnace or the like and having a fail-safe feature for that use.

It is also an object of this invention to provide a flame detector switch such as may be used in a flame alarm system and having a fail-safe feature for that use.

Other objects and'features of this invention will become obvious upon a further reading of this specification especially when taken in view of the accompanying drawings in which:

FIG. 1 is an isometric view of one embodiment of this invention.

FIG. 2 is a partial section view showing the fastener assembly of the embodiment of FIG. 1.

FIG. 3 is a side view, partially in section, showing a second embodiment of this invention.

Briefly the flame detector devices of this invention comprise a switch having a plunger for actuation with a ceramic tube and means for supporting the ceramic tube in axial alignment with the plunger. A metallic rod is disposed within the tube extending the length thereof with one end terminating adjacent the plunger. Means are provided maintaining the tube and the end of the rod not adjacent the plunger in fixed spatial relationship with one another and with the switch plunger. Thus, the free end of the rod is axially translatable responsive to changes in temperature to actuate the switch at predetermined temperatures.

Referring now to FIGURES 1 and 2 for a detailed description of one of the devices embodying the teachings of this invention, there is shown a switch having a plunger 12 and an actuator assembly 14 attached to said switch.

The actuator assembly 14 includes a U-shaped bracket 16 attached at the end of its respective arms 18 to the switch 10 by means of the bolt and nut arrangement 20. The arms 18 of the U-shaped bracket extend beyond the tip of the switch plunger 12 so that the base 22 thereof passes adjacent and perpendicular to the plunger. The bracket base 22 defines an aperture 24 (FIG. 2) in axial alignment with the switch plunger 12.

A ceramic tube 26 closed at one end 28 and having a flange 30 at its other end extends through the aperture with the flange 30 maintaining the open end within the bracket 16 adjacent the plunger 12. The tube 26 is formed of a refractory material having a low coefficient of thermo-expansion such as for example quartz or ceramic.

3,243,557 Patented Mar. 29, 1966 ICC Within the tube 26 is a rod 29 of a material having a coeflicient of thermo-expansion substantially greater than that of the tube 26. A metallic material such as stainless steel is to be preferred. One end 29a of the rod is in abutment with the closed end 28 of the ceramic tube 26 while the other end 29b extends through the open flanged end 30 of the tube to terminate adjacent and in line with the switch plunger 12.

A stainless steel sleeve 31 surrounds the tube 26 and is fastened at its flanged end 32 to the bracket base 22 by any convenient means such as a weld or the like. A ferrule 33 surrounds the sleeve 31 and has a threaded internal surface 34 which cooperates with an externally! threaded fitting 34a (such as shown in FIG. 3) and a sealer ring 34b to maintain the ceramic tube clamped to said sleeve 31. The fitting 34a is fixed to the Wall 35 of the structure enclosing the temperature measured chamber and its threaded engagement with ferrule 33 supports the whole assembly of the switch 10 and actuator 14 thereto.

A second bracket 36 is secured to the switch by the nut and bolt arrangements 20 along with the additional nut and bolt arrangement 20a. The bracket has a shallow channel portion 38 with depending cars 40 to hold the ends of a leaf-spring type resilient member 42.

The leaf spring 42 is in resilient engagement with the end 2% of the rod 29 so as to constrain the other end thereof 29a against the closed end 28 of the tube 26.

A bolt 44 extends through aperture 43 in spring 42 and confronting apertures 43a in the brackets 16 and 36 with a nut 46 threaded thereon to maintain the brackets in fixed spatial relationship with each other.

The device shown in FIGURES 1 and 2 operates as follows to detect a flame or excessive temperature. The spring 42 maintains the rod in abutment with the closed end of the ceramic tube at 26 so that the flange 30 at the open end of the tube is held constrained against the base portion 22 of the U-shaped bracket 16. Thus the ceramic tube 26 and the end 29a are positionally fixed with respect to one another and with respect to the switch plunger 12.

When a flame is detected the heat therefrom passes through the ceramic tube 26 to the stainless steel rod 29. The tube 26, of course, is not materially affected by the heatbut the stainless steel rod 29 is caused to expand, especially in a longitudinal direction. The end 29b will thus move towards the switch 10 to eventually actuate the plunger 12 and operate the switch to indicate the present of a flame.

This type of switch is especially useful for detecting the flame in the combustion chamber of a furnace. It is important that there be some means of detecting the presence of a flame as a safety feature to control the fuel feed thereto. That is, if the furnace is turned on but a flame is not produced, the fuel feeding mechanism should be disengaged to eliminate the possibility of explosions in case the flame is later ignited.

The device hereinbefore described is fail-safe when used in a furnace as hereinbefore described. If the ceramic tube breaks for any reason, it will be noted the spring 42 will tend to urge the rod 29 away from the switch plunger 12 to indicate a flame o-ut condition.

Reference is now made to FIGURE 3 showing a second embodiment incorporating features of this invention. This device is fail-safe in the other direction as will be seen, so that it may be advantageously used in applications such as a flame alarm system.

This embodiment includes the identical type switch 10' with the plunger 12 to which is attached a U-shaped bracket 16' almost identical to the U-shaped bracket of the first embodiment. The only difference in the bracket is the size of the aperture 24 which is sized to just admit the stainless steel rod 29 but not the hollow ceramic tube 26'.

The ceramic tube 26 is open at both ends and the stainless steel rod 29' has a cap 31' is threaded at 29b into the end of rod 29. The cap 31' is in engagement with thedepending end of the tube 26'. A helical spring 52 constrained between the base 22' of the U-shaped bracket 16 and a C-washer locked within an annular groove (not shown) in the tube end 29b maintains the cap 31' in engagement with the tube 26'.

A similar ferrule, sleeve and fitting arrangement is used to secure the tube 26' to the bracket and the whole assembly to the wall of the chamber being measured. This device also includes a bracket 36 similar to bracket 36 in FIG. 1 which serves to strengthen the assembly in conjunction with the spacer nut 46' and bolt 44.

Normally, this configuration operates to detect the presence of a flame by virtue of the thermo-expansion of the stainless steel rod 29' with respect to the ceramic tube 26'. The end 29a is held fixed with respect to the switch plunger 12' and the end of ceramic tube 26', axial expansion causing the end 29b to actuate the plunger 12'.

As previously mentioned, this device will indicate a flame-on condition in case of damage to the ceramic tube 26. If the tube breaks for some reason, the constraining spring 52 urges the rod towards the switch to actuate the plunger 12' indicating a flame-on condition. Thus, this embodiment is ideal for applications to detect the presence of flame in a fire alarm system or the like.

While detailed descriptions of two embodiments have been made herein, it is recognized that many modifications may be made thereto while remaining within the spirit of the present invention. Therefore, it is intended that this patent be limited only by the scope of the appended claims.

What is claimed is:

1. A temperature operated actuator for a switch having a plunger for actuation comprising a ceramic tube, a metallic rod within said tube having one end extending beyond one end of said tube and having a cap on the other end in abutment with the other end of said tube, means for supporting said tube with said one end of the rod adjacent the plunger, and means for maintaining said tube cons-trained between said end cap and said supporting means.

2. A temperature operated actuator for a switch having a plunger for actuation comprising a support attachable to the switch and having an aperture in axial confrontation with said plunger, a ceramic tube with a cross-sectional area greater than the cross-sectional area of said aperture having one end in abutment with said support about said aperture, a metallic rod within said tube having one end extending therebeyond through said aperture to abut the plunger, a cap on the other end of said rod in abutment with the other end of said tube, and means for resiliently constraining said tube in normal abutting relationship between said support and said cap.

3. A temperature operated actuator for a switch having a plunger for actuation comprising a support attachable to the switch and having an aperture in axial confrontation with said plunger, a tube of material having a relatively low coeflicient of linear expansion with a crosssectional area greater than the cross-sectional area of said aperture, said tube having one end in abutment with said support about said aperture, a rod of material having a relatively high coefficient of linear expansion within 4 a C-washer within said groove, and a helical spring about said rod between said C-washer and said support to maintain said tube in normal abutting relationship between said support and said cap.

4. A temperature operated actuator for a switch having a plunger for actuation comprising a support attachable to the switch and having an aperture in axial coufrontation with said plunger, a refractory material tube with a cross-sectional area greater than the cross-sectional area of said aperture having one end in abutment with said support about said aperture, a metallic rod within said tube having one end extending through said aperture and in abutment with the plunger, a cap on the other end of said rod in abutment with the other end of said tube, said rod having an annular groove adjacent said one end, a C-washer within said groove, and a helical spring about said rod between said C-washer and said support to maintain said tube in normal abutting relationship between said support and said cap.

5. A temperature operated actuator for a switch having a plunger for actuation comprising a support attachable to the switch and having an aperture in axial confrontation with said plunger, a ceramic tube with a crosssectional area greater than the cross-sectional area of said aperture having one end in abutment with said support about said aperture, a stainless steel rod within said tube having one end extending through said aperture in abutment with the plunger, a cap on the other end of said rod in abutment with the other end of said tube, said rod having an annular groove adjacent said one end, a C-washer within said groove, and a helical spring about said rod between said C-washer and said support to maintain said tube in normal abutting relationship between said support and said cap.

6. A temperature operated actuator for a switch having a plunger for actuation to be mounted on a structure wall, or the like, comprising a support attachable to the switch and having an' aperture in axial confrontation with said plunger, a ceramic tube having a closed end and an open end with a flange about said open end, said tube extending through said aperture with said flange in abutment with one side of said support, a sleeve surrounding said ceramic tube having one end fixed to the opposite side of said support, a ferrule surrounding said sleeve and having internal threads therein, a fitting adapted to be attached to the structure wall having an aperture therethrough for receiving said sleeve and external threads for cooperative engagement with said internal threads, a sealing ring surrounding said sleeve between said fitting and said ferrule for deforming said sleeve to clamp said tube there within, a stainless steel rod within said tube having one end abutting said closed end and the other end adjacent the plunger, said support including bracket means and a leaf spring held at its ends by said bracket means with a middle portion thereof passing between the other end of said rod and said plunger, said leaf spring constraining said rod against the closed end of said tube.

References Cited by the Examiner UNITED STATES PATENTS 1,990,747 2/1935 Netschert 200-l37 2,640,129 5/1953 Starbird 200137 2,640,896 6/1953 Cataldo et al 200-137 2,705,746 4/1955 Strange 200-l37 3,162,742 12/1964 Vicenzi et a1. 20013'7 BERNARD A. GILHEANY, Primary Examiner.

L. A. WRIGHT, Assistant Examiner. 

1. A TEMPERATURE OPERATED ACTUATOR FOR A SWITCH HAVING A PLUNGER FOR ACTUATION COMPRISING A CERAMIC TUBE, A METALLIC ROD WITHIN SAID TUBE HAVING ONE END EXTENDING BEYOND ONE END OF SAID TUBE AND HAVING A CAP ON THE OTHER END IN ABUTMENT WITH THE OTHER END OF SAID TUBE, MEANS FOR SUPPORTING SAID TUBE WITH SAID ONE END OF THE ROD ADJACENT THE PLUNGER, AND MEANS FOR MAINTAINING SAID TUBE CONSTRAINED BETWEEN SAID END CAP AND SAID SUPPORTING MEANS. 